Johny - I know you sent your phone number in one of your missives and I am sorry I've not reached out to yet. We broke our centerboard the other day and its been keeping me quite busy.
In any case -Spartite 2000 has a Shore Hardness of 55-60D. The WylieCats use it to hold their carbon fiber mast in place. I used a product from Smooth-On - see here http://www.smooth-on.com/Urethane-Plastic-a/c5_1120_1208/index.html. You definitely want to cover ANYTHING that you don't want to have the product stick to with a demolding agent - SpareTite recommends petroleum jelly. Also, there shouldn't be anything that the will cause the casting to "key in" and make removal hard. Building a mold is important, too. I got Tap Plastics to cut me a PVC sheet with a 10" hole - the diameter of my mast, that I put at the bottom of the mast collar. The deck was at a slant, so I used moulding clay to build a dam. One of the old fiberglass wedges worked to hold the mast in place and I cast 1/2 diameter at a time. I was able to remove each piece, trim to size/clean up and re-insert.
I didn't looked at the Polytek.com website for too long but it seem like all their products were too low in harness.
For kicks here is a hardness comparison scale.
Feel free to ask any more questions. Best of luck :)
Erik
